


Sizing Up

by Bloodsbane



Category: The Magnus Archives (Podcast)
Genre: Canon Asexual Character, Crack Treated Seriously, Dildos, Exhibitionism, Humor, M/M, Martin is a Size Queen, Partial Nudity, Sex Toys, Trans Jonathan "Jon" Sims | The Archivist, Trans Martin Blackwood, Voyeurism, ace flavor: neutral/favorable, it's a bit ambiguous but jon doesn't participate in anything so yknow
Language: English
Status: Completed
Published: 2020-10-10
Updated: 2020-10-10
Packaged: 2021-03-08 03:01:36
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,154
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26938573
Author URL: https://archiveofourown.org/users/Bloodsbane/pseuds/Bloodsbane
Summary: After accidentally discovering one of Martin's sex toys in the shower, Jon has questions. This leads, unexpectedly, to an argument, and before Jon knows it, he's getting a bit of a show.---Basically, Jon doesn't think Martin can actually fit a huge dildo inside of him. Martin is determined to prove him wrong.
Relationships: Martin Blackwood/Jonathan "Jon" Sims | The Archivist
Comments: 15
Kudos: 284





	Sizing Up

**Author's Note:**

> OKAY SO. This was inspired directly from a very silly comic I drew months ago. I'll provide a link to said comic in the end notes once it's been reposted on my ao3. It was just done for a laugh, but I've been wanting to write something very silly lately, and kept thinking this would be a really funny scenario. It was a lot of fun to write! 
> 
> (I'd like to note: the exact size of Martin's dildo is kept purposefully ambiguous, so feel free to imagine it as big as you'd like~)
> 
> CWs:  
> > minor secondhand embarrassment (resolved pretty quickly)  
> > slightly under-negotiated kink  
> > consent checks
> 
> terms used for martin are: cock/cunt/hole
> 
> (special thanks to semnai and tree for beta reading!)

Martin Blackwood wouldn’t have ever been Jon’s first choice for who to spend a weekend with - probably not even his second or third. He was, however, the first person to offer him a couch when Jon explained his flat was being treated for termites. It was an issue he hadn’t even been aware of until the night before, when he found the notice taped to his door. So, last minute, he needed to find a place to stay. **  
**

Sasha was going to be out of town; Tim already had quite a few roommates and no extra space. Jon would have texted Georgie as his last resort, but then Martin said he wouldn’t mind if Jon wanted to stay at his. Jon had never been to Martin’s flat, even now, as their relationship was slowly evolving beyond pure professionalism. The three archival assistants seemed quite determined to assimilate Jon into their little friend group, and it was forcing him to reconsider some -- evidently unwarranted -- assumptions he’d had about Martin. 

So no, Martin wasn’t his first choice, but Jon hadn’t been too bothered by the prospect of staying at his place. He didn’t expect much to happen or any trouble to crop up. Martin was, if nothing else, polite, and seemed like he would be a good host.

It should have been a relatively uneventful stay. 

And it probably would have been, too, if Martin hadn’t needed to visit his mother unexpectedly near the end of Friday. He’d popped into Jon’s office and given him a spare key, telling him he was welcome to head to Martin’s flat on his own. 

The idea didn’t appeal to Jon -- it felt awkward being in someone else’s home without them around. But it was late in the day and he was tired, his back hurt, and he wanted food. So he headed out at a surprisingly reasonable time, given his track record. 

Reluctant to make food in someone else’s house without their permission or presence, Jon decided he’d spend most of his time waiting for Martin by taking a shower. He needed one anyway, and unlike cooking, he felt more comfortable bathing without someone else nearby. 

The plan had been to shower. Instead, Jon ended up sitting on the sofa in something of a stupor until Martin got home.

“Hello?” Martin called out shyly, closing the door. “Jon?” 

“I’m here,” Jon said. When Martin came into view, head tilted in a silent question, Jon explained, “I, uh. I saw something that perhaps I wasn’t meant to see.”

Immediately, every inch of Martin grew tense. He asked, “And what is that…?”

“In the bathroom.”

Martin’s brow wrinkled.

“In the shower,” Jon elaborated, feeling his face grow hot as he remembered what he saw. “On the wall.” 

Pretty soon, Martin’s the one red in the face. It was quite interesting to watch, actually, the way his skin flushed all the way to his ears. “O-oh.”

“Yeah.” 

“I- I am _so_ sorry Jon,” Martin told him, looking mortified. The back of his hands went up to his face, to cool his cheeks, or perhaps it was an attempt to hide. “God, I- I didn’t think- I just, forgot-”

“It- it’s fine,” Jon told him. Because, in truth, it really was fine. Jon certainly hadn’t expected to be confronted with… _that…_ while trying to use the shower. But it wasn’t like he didn’t know some people used things like that, and even if he wasn’t interested in the why aspect, he wasn’t about to judge. It’s just unfortunate for both of them he stumbled on something he wasn’t meant to see. But there is something he’d seen, something incidental, that he couldn’t bring himself to stop thinking about it. He’d even peeked back in the bathroom, past the curtain, to make sure he’d seen it correctly. 

Now, Jon cleared his throat and said, “In all honesty, I would have just… pretended not to have noticed, except that, um…” 

Martin, eyes wide, stared back at him. “Except what?” 

“Well. I was a bit curious...” Jon felt the way his voice was faltering, but couldn’t help it. Saying something like this was embarrassing, not to mention totally inappropriate, given their relationship, but… he really wanted to know. “Why, uh… Why that big?”

“Jon!” Martin whined, turning away and hiding fully behind his hands. 

“I’m serious! I mean, it’s, ah, quite large-”

“You’re going to kill me,” came the muffled, agonized groan. 

“I just don’t understand why you’d get one that big,” Jon said, feeling much too hot, “when you won’t even be able to use all of it.” 

After he said this, there was a brief pause. No more little noises of distress from Martin, who was still turned away slightly, hidden from Jon’s eyes. Then he turned around and peeked at Jon through his fingers. “What do you mean?” 

“What do you mean, what do I mean?” Jon asked, feeling a familiar annoyance sneak its way past his embarrassment. “I mean that the… the phallus-”

Martin actually _giggle-snorted_ , so abruptly it seemed to catch them both off guard. “Jon, god, Jon, just say dildo, oh my god.” 

“The dildo is, frankly, ridiculously large,” Jon informed with extreme solemnity. Martin was still blushing, but now there was a wobbly grin forming behind his hand. “It looked to be nearly the size of my entire forearm, Martin. It’s too big! There’s- there’s no way you could put the entire thing in, so, so I don’t understand-”

“Wait, you really think that?” Martin interrupted. He was facing Jon again, hands falling to his sides. He didn’t look so shamefaced anymore, rather, he seemed genuinely interested in what had somehow become an earnest discussion about… his sex toy. 

“Of course! It’s- comically large.” 

“It’s not _that_ big,” Martin protested, and actually rolled his eyes at Jon. “I mean, yeah, it’s big, but I can handle it.” 

“I somehow seriously doubt that,” Jon stated, crossing his arms. “There’s no way.” 

“Yes there is,” Martin insisted, and took a step closer. “Look, I mean, I’m a big guy, aren’t I?” 

“But still!” 

“I think I would know whether or not it was too much,” Martin said flatly. 

Jon didn’t know what to say to that, so he simply shook his head. It was- no, ridiculous. There was simply no way. 

He expected the subject to drop, but Martin was surprisingly indignant. “I can’t believe you think I’m making this up!” he said, hands on hips. “What, do you need a demonstration or something?” 

“Pardon!?” Jon stared at Martin, feeling like he’d just stepped into freezing water, his entire body shocked. 

Martin laughed at his reaction. “God, your face!” 

Feeling quite nettled, Jon couldn’t help but snap, “It wouldn’t do any good, anyway, because you wouldn’t be able to take it.” 

There was a moment of silence. Martin’s face shifted, slowly, into something intimidatingly serious. Finally, he said, “You want to bet on it?” 

“...W-what?” 

There was something about Martin, nearly imperceptible, that made Jon realize he had somehow sent them careening down an unexpected path. It was in the stubborn set of his mouth, in the glint of those brown eyes. 

“Stay right there,” Martin said, and then abruptly left. He went down a hallway, one Jon could only assume led to his bedroom. Jon, baffled, weighted down with a vague sense of impending consequence, obeyed Martin’s command. 

About ten minutes later -- or was it fifteen? Jon had been staring down at his hands the whole time, idly fidgeting -- before Martin emerged from his bedroom. Only now he wasn’t wearing jeans anymore. Jon sputtered, but Martin barely spared him a glance before walking straight into the bathroom. Jon heard an odd sound, one that echoed faintly through the doorway, and he only had about two seconds to realize what it was before Martin came back into view. 

In Martin’s hands was the dildo. It was lengthy, hefty, and a rich shade of magenta. It had ridges leading from the base to the slightly tapered tip. Now that Jon was looking at it under better lighting, he realized it glittered. It also had a significant swell near the base. 

“Um.”

“Here is what we can do now,” Martin told him, looking positively mischievous. “We can go into the kitchen, and I can take this in front of you-” 

Jon made a faint choking sound. 

“-or, if you’d prefer, you can simply admit that I would definitely know what I can and can’t handle taking into my own body, and apologize for calling me a liar, and we can forget this whole thing ever happened,” Martin finished, perfectly pleasant. 

Jon frowned at that, scrunching up his nose. “I never called you a liar.”

“You were implying it.”

“I was merely stating a fact. There is no way you can take that thing-” he stated, pointing at the offending piece of silicone, “-inside you. Not all of it.” 

“Can too.”

“You cannot!” 

“Can so~” 

Jon grit his teeth. Martin’s tone, nearly flippant and sing-songy, reminded him far too much of certain children he’d mentally cursed and sworn vendettas against in grade school. 

Sealing their fates, Jon pushed himself up from the sofa. “Fine then! Fine. Show me.” 

Martin smirked. “You sure? I get full permission to rub your nose in it once I prove you wrong.” 

“Only you won’t,” Jon said, walking into the kitchenette. It was a space with tile floors and a small round table just big enough for two people to share. Jon took a seat in one of the wooden chairs, crossing his legs at the knee, arms still folded over his chest. 

Martin followed him to the kitchen, but stood a few feet away. He was inspecting the floor with a vague grimace. “This won’t be super comfortable,” he mumbled, but didn’t seem too perturbed. After a moment of consideration, he knelt down on the balls of his feet and then pressed the toy into the floor until the suction cup secured it. The dildo stood fairly erect on its own when Martin took his hands away. Jon felt as if the bright instrument was somehow mocking him, or maybe threatening him. 

“Be right back!” Martin said, then scurried back into the bathroom. Jon continued his glaring contest with the toy until Martin returned. There was a bottle of lubricant in his hand, which gave a cheerful _pop!_ as Martin flipped the lid open. It was then that Jon realized what exactly was about to happen. 

He was sitting in Martin Blackwood’s flat. Martin Blackwood, his co-worker -- his assistant, his subordinate -- was currently slathering lube all over his personal sex toy. Jonathan Sims, Head Archivist of the Magnus Institute, London, was about to watch Martin Blackwood attempt to take the entirety of a huge sparkly suction-cup dildo inside him. 

To prove a point. 

Jon forced himself to open his mouth, intending to- to protest, or at least to tell Martin to _wait, just a second-_

Then Martin took his pants off, and Jon’s words disappeared. 

The space between Martin’s legs was glistening, just slightly -- he was already wet. Jon thought back on Martin disappearing into his room for a while, then realized what must have happened. Had he really, actually gone off to finger himself open? That was before Jon even agreed to this bet! 

Martin kicked his briefs off to the side, then set the lube on the floor as he settled onto his knees. He sat in front of the dildo, hiding it from Jon’s view. His eyes snapped up to meet Jon’s. “Ready for a show?” he asked, cheeks rosy red, a slight breathlessness to his voice.

Jon closed his mouth, hands twisting together on his lap, and simply nodded. 

First, Martin brought two fingers down between his legs. He briefly fingered his cock, already swelling, slick and red as it peeked from between his fingers. Then his fingers traveled down, past pink lips, until they were able to curl and slip inside. Martin took them with ease, barely making a sound. Instead it was Jon who inhaled sharply. But the sound of his breath couldn’t cover the sounds of Martin fingering himself, carefully rocking his hips, his fingers pulling out only for a third to join them on their way back in. 

“That- that should be good,” Martin panted, pulling his fingers out. They were shiny and slick and Jon wanted to look away, feeling very shy for someone who’d just watched someone finger themselves open. 

The hand went back to the dildo, giving it a few pumps. Making a vague noise of dissatisfaction, Martin reached over for the lube again. He reapplied a bit to the toy, then stood, staring down at it. “Hmm.”

“Um…” Jon had to spare a moment to lick his lips, mouth feeling very dry. “Is something wrong?” 

“It’s just easier to do this in the shower,” Martin said quietly, frowning a bit. “When it’s on the wall…” Then he shook his head and shrugged. “This is going to destroy my calves, but okay.” 

Then Martin was kneeling, one hand supporting himself, the other carefully guiding the dildo to his- his hole. Jon felt himself grow hotter and hotter the closer Martin came to penetrating himself. He wasn’t sure if the sensation racing up and down his back was arousal or not, but it did make him feel a bit breathless, a bit dazed. He tried not to think too hard about it, merely focused on his job of watching Martin. 

The tip slid in easily, but Martin still paused after about an inch. Already, Jon could see the way his thighs gently trembled. Martin’s face was flushed, and his breathing was getting more erratic. Then, slowly, he began to sink down. 

The next pause didn’t come until he’d taken it halfway, and it was a bit easier for Martin to adjust his position and distribute his weight better. He was making little sounds, now, at the end of every breath - moans, perhaps. Jon squirmed in his seat, but stayed silent, waiting. 

Before taking any more, Martin slowly, carefully, rotated his hips. He couldn’t lift them too far without fixing his posture again, but Jon could see the way his motions pulled the dildo out, just a bit, before he would swing around and take it back inside. The noises were becoming more frequent, and sweeter, and Jon could feel himself slipping into a sort of tunnel vision. It felt like nothing existed beyond the beat of his heart and the sight of Martin stretching himself open, taking the dildo into him by the slightest of degrees. 

Before Jon knew it, Martin had taken a majority of it inside. His knees were on the tile now, spread wide, and both hands behind him, supporting his weight. The only thing left between him and a decisive victory was the round swell at the base of the toy. 

Jon could see the way Martin was already stretched; he could see the way the toy was dominating the space inside of Martin. He could see how much of the lubricant had been replaced with Martin’s own slick, enough that there was a tiny puddle growing on the floor just beneath him. 

Martin had been reduced to heavy pants and trembling legs. Every inch of bare skin that Jon could see was flushed. His expression had clouded somewhat, eyes growing less focused the more he took. Yet, still, he turned his head up to make eye contact with Jon. “How- how are you holding up- over there?” he asked between shaky breaths. 

Jon shifted, enough for the heat in his body to unsettle, lighting up his nerves. “I, uh, I’m fine. Are- are you fine?” 

“I’m…” Martin let out a shaky laugh, almost too fragile to be anything more than a whine. “I’m fine, it’s just, ah, this- this last bit is always the trickiest.”

“Ah.” 

“Just a second…” 

Martin caught his breath. With clear effort, he began to lift himself up and down on the toy, very gently fucking himself. The sight made Jon squirm with anticipation. Every time Martin’s cunt met the top of the swell, he could hear Martin’s tiny little noise, like a huff, frustrated maybe, or simply pleased by the feeling of it. 

Then, after a few seconds of this, Martin pushed down. He rotated his hips, he arched his back, and Jon could see very, very clearly, slowly but surely… 

He took the rest. 

Jon watched the toy disappear until all there was left to see was the suction cup base. Everything else was inside of Martin, who let out a heavy gust of breath, as if he’d been holding it. “F-fuck,” Martin groaned, and Jon blushed furiously. 

Once Martin had his wits about him, he carefully sat up straight. He looked… It almost looked like he was simply sitting on the floor. On the kitchen floor, pantsless, for no reason, kneeling before Jon. After a moment of self-assessment, Martin put his fists triumphantly on his hips and gave Jon a cocky little smirk. “See? I told you!” 

“I…” Jon was, to be frank, flabbergasted. “How…?” 

“It just takes a bit of practice,” Martin told him, sounding a little breathless. “Practice and patience and a- a lot of lube.” 

“Ah. And… It, uh.” God, why the hell was he still feeling embarrassed? “It doesn’t… it doesn’t hurt?” 

“Nah, not really,” Martin told him. “I mean, I’m being pretty still now too, so I- I feel it, obviously I know it’s there-”

“If you told me it was barely noticeable, then I’d really have to call you a liar,” Jon interrupted. 

Martin laughed, but the sound got cut off by a hitched breath. He squirmed a little where he sat. Jon remembered the reality of the situation. 

It seemed Martin did, too, for he grew very red and said after a few seconds, “Um… hah, I uh, I sort of… didn’t think about this beyond the whole ‘I told you so’ bit.” 

Martin gave a weak laugh, clearly flustered, but Jon laughed too, and it was very strange, how light the mood felt between them. Jon supposed it was far too late to try and act like this wasn’t a totally ridiculous situation they found themselves in. 

And, if that was the case, then Jon didn’t really mind leaning into it. 

“Do you…” Jon flapped a hand, blushing. “Would you like to, uh… finish?” 

“Wh- are you serious?” 

“I mean, you’ve already got it in,” Jon said, humor in his voice. “It strikes me as a bit of a waste, to- to take the whole thing and then not, well, conclude.” 

_“Conclude.”_ Martin shook his head, giggling. “Your pillow talk is awful, truly, just the worst.” 

Jon scowled, but that only made Martin giggle harder. “Look, I’m just saying if you’d like to orgasm, I won’t be stopping you.” 

Martin’s laughing petered out rather abruptly, and he made a sound almost like a moan. Peeking at Jon through his bangs, he asked, “And… You’d be fine just watching?”

“I don’t mind watching,” Jon confirmed, his voice quiet. 

Even just that seemed to do something to Martin, who rocked his hips and whimpered. “Y-y'know, I didn’t know I even liked that,” Martin panted. “Being watched, I mean.”

“Oh, really?”

“Yeah. I, I didn’t mean it before, when I said it, but- but actually, after I suggested it -- just as a joke, honestly -- I realized that I thought the idea of showing you, and having you watch me t-take it all, it was- was really hot, actually,” Martin confessed. “That’s- ah- why I went to my room first, uh, I was… already kind of excited, and I-” 

“You touched yourself?” Jon asked. He’d already suspected, of course, and felt vindicated at having it confirmed. 

“Yeah…” 

“You liked the thought of me watching you like this?” 

“Yeah,” Martin groaned, eyes fluttering closed. His hands moved in front of him, the angle of his body changing so he could properly ride the toy. Jon couldn’t quite see the way it would disappear into Martin, over and over, but he could hear it. 

“And do you still like it?” Jon asked, softly, as if he could break the moment if he spoke too sharply or too loud. 

Martin couldn’t speak, could only nod frantically as he picked up speed. By now he was moaning openly, and Jon could see from his movements that he was close. He tried to think of how to help his assistant along. 

Oh, maybe that. “I have to say, Martin, I certainly wasn’t expecting my evening to take such a turn,” Jon told him, which was honest enough. “To think I’d have my assistant kneeling at my feet, doing something like this so shamelessly.” 

“F-fuck-!” Martin let out a harsh breath, then keened sharply as he came. Jon could see the way his entire body jolted with it. Martin’s hand flew to his cock, pressing at it in time with the rocking of his hips, drawing the orgasm out for as long as he could. Now Jon could see, just slightly, the way his cunt was clenching around the toy, and he could even see the vaguest impression of it moving inside through Martin’s stomach. 

Almost abruptly, Martin came to a stop. He was shivering, trying to catch his breath. Jon stayed completely still, feeling a bit like he’d been set on fire. 

Eventually, as Martin’s breathing became a bit more even, Jon asked, “Are you alright?”

“Wh- I- y-yeah,” Martin said. After another moment, he brushed his hair from his face and looked up at Jon. His eyes were losing the cloudiness, and now sparkled; it made him look vivacious and handsome. “And you? You- do you need anything?”

“Oh, no, I’m- I’m perfectly fine,” Jon assured him. There was the faintest beat of arousal humming beneath his skin, but it was easy to ignore and wasn’t important to him. “That was… quite something.”

Martin gave a weak laugh. “I- I guess it was. Oh, god, uh.” Martin shifted a bit, his breath hitching, but Jon mostly noticed the way his legs were trembling. After a moment, Martin seemed to give up whatever he’d been doing. He had composed himself a bit since hitting his peak, but the blush was returning in full force. Looking quite shy, he held his hands up toward Jon. “I, um, I don’t think I can stand on my own like this…” 

“Oh! Yes, one moment.”

Jon hurried over from where he’d been sitting and held out both hands. Martin gripped them in his own. His hands were relatively cool, but as Jon slowly helped him to stand -- as he got closer -- Jon could feel Martin’s body heat. It was almost enough to distract him from the wet sound of Martin pulling himself off of the toy.

Martin seemed a bit dizzy and weak once he was standing, but capable of balancing himself. Jon would have been fine pulling away, letting his hands fall back to his sides, or perhaps crossing them. He was feeling oddly vulnerable now that things had finished. 

It must have shown on his face, because Martin took a careful half-step back and asked, “Are you sure you’re alright, Jon? Things got… uh, a bit intense?” 

“I’m… I’m fine, Martin, really.” After thinking it over, Jon admitted, “This was… sort of fun?” 

Martin laughed, and Jon could feel it where their hands met. “I mean- yeah! Yeah, it kinda was, huh? Um, are you sure though? I…” He glanced away, looking self-conscious. “I didn’t mean to put you on the spot or anything, really, I just got kind of caught up?”

“It’s alright, Martin,” Jon told him, trying to inflect some authority into it, hoping that would help. 

Perhaps it did; instead of asking again, Martin turned his gaze to the toy on the floor. “I should probably take this back to the bathroom? And clean it off.”

“Ah-” Jon huffed a laugh, pulling away as Martin carefully knelt back down to pull the dildo off of the floor. “Yes, that makes sense. I’ll leave you to it, then.” 

“Thanks. Um…” Martin stood before Jon, holding the -- still rather damp -- toy with both hands. “Would- do you- I mean, uh… Do you wanna… join me?”

“...Pardon?”

“In the shower? You were going to use it earlier, right? Just- it would be fine with me, if you wanted to, and- I don’t mean anything untoward, obviously -- of course! -- it just, uh… It saves water, too…” 

Jon considered him and the offer. Then he said, as deadpan as he could manage, “Well, if you think all three of us could fit in there.” 

It took a moment for Martin to get it. Then he giggled, and snorted again, and told Jon to shut up as they headed for the bathroom. 

**Author's Note:**

> hope you enjoyed~


End file.
